The South Pacific Forum (SPF) has consolidated regional cooperation as an effective mean to increase regional security since its formation in 1971. In the 1990s, SPF started to diversify regional cooperation by extending its commitment to other forms of regionalism. One of the salient cases is the commitment in Asia-Pacific regionalism, notably Asia-Pacific Economic Cooperation (APEC) which was created in 1989. This paper investigates the reasons and nature of the SPF which is going to get involved in the macroregional frameworks of the Asia-Pacific. As mentiond above, SPF has played a significant role in increasing regional security. In the economic domain, the coordination of aid and the facilitation of negotiations on trade preferences as well as the price stabilization scheme for the Pacific Island Countries can be singled out as the SPF's major contributions. However, in the 1990s, new developments appear and threaten regional economic security of SPF. They are categorized into three issues: 1) the uncertainty of aid; 2) the formation of a new international economic order; 3) the emergence of macroregional economic blocks. These three threats to regional economic security urged SPF to diversify regional cooperation. The commitment to APEC is one such diversifying endeavour to respond to the threats. It is expected that SPF's commitment in APEC will increase as years go by. Consequently, the linkages between SPF and APEC will be much enhanced. However, some problems can be pointed out in the future relationship. They are: 1) relations between SPF and individual countries; 2) two trends in APEC, that is, trade and aid; 3) SPF's ambivalent interests in trade liberalisation and trade preferences. These problems can not be ignored when SPF gets seriously involved in APEC.